1. Field of the Invention
The present invention relates to communications networks and, more specifically, to determining protection resource sharing opportunities such as within a large-scale wavelength-division multiplexing (WDM) mesh network.
2. Description of the Related Art
Optical transport networks today are increasingly being designed, deployed, and provisioned as mesh networks with shared path protection. Typical mesh network designs include path protection based on the assumption of a single node or link failure in the network. This is a reasonable assumption for high-availability nodes, given the low probability of link cuts or failures. However, such design assumptions do may not adequately allow for the possibility where failures are not independent random events, such as catastrophe scenarios or planned and coordinated attacks which might involve multiple failures occurring in a compressed timeframe. As such, there is a need by defense and civil agencies for robust high-speed backbone landline networks resilient to multiple failures. However, one of the major challenges of designing a multi-service network robust to multiple failures is providing the needed redundancy in a capacity- or cost-efficient manner. Thus, capacity sharing is desirable within the context of network design and provisioning so that the resource necessary to support a demand flow (i.e., demand) of a path remains satisfied in the event of link or node failures. Of particular interest is capacity sharing within a large scale wavelength-division multiplexing (WDM) mesh network.
One approach to shared protection is finding, for each optical resource demand flow, two node-disjoint lightpaths between source and destination nodes (i.e., one for the primary path and one for the backup or protection path). Such disjoint paths offer the advantage of not requiring fault isolation and thus tend to provide faster restoration compared to alternative approaches. When planning and/or provisioning capacity for protection against single node or link failures using node-disjoint paths, two demands can share protection capacity if the primary paths of the two demands are node disjoint and the underlying graph topology allows link intersection of the backup paths. This design is based on the assumption that, after one such failure anywhere in the network occurs, the remaining resource demands are not expected to have protection and therefore forfeit their guarantee to restoration from a single failure (i.e., the remaining resource demands are “demoted” from 1-protected to unprotected). Otherwise, if each resource demand must be restorable after one failure that only directly effects it, the restoration bandwidth must be dedicated. Since the primary paths are disjoint, no single failure will simultaneously effect both demands, and since no protection for the second demand is required after any one failure in the network, then the two demands can share protection bandwidth.
Another approach to shared protection is where the bandwidth of a failed primary path is made available for restoration of other demands. This is referred to as primary reuse or stub release; specifically, the releasing of capacity of the primary path of a demand effected by a failure for reuse by other demands for restoration. One drawback to primary reuse is that such reuse may preclude reversion (i.e., restoration of the failed demand to the original primary path once repairs to it are completed). However, due to the complexity in the control plane of implementing reversion, networks using shared meshed path protection either allow or preclude primary reuse, but typically does not implement reversion.